Pulp and paper manufacture requires the use of large volumes of water. With ever higher antipollution standards and increasing cost of water, it has become necessary to treat the resultant waste water, or effluent, from such operations to control the biological oxygen demand (BOD), color, temperature, and pH thereof prior to its discharge into a watercourse, such as a river, lake, stream, pond, or the like.
While the temperature and pH of the effluents can generally be economically and readily controlled and brought within requisite standards and the BOD also controlled by present techniques, it has not been possible to satisfactorily and economically remove the color bodies from such effluents.
One procedure that has proven operatively satisfactory to remove the color bodies is the ultrafiltration process and system set forth in U.S. Pat. No. 3,758,405. However, such process and system have not been entirely satisfactory for commercial purposes because of cost. The cellulose acetate membranes used have short operational lives due to degradation caused by high heat and high pH and must frequently and with difficulty be cleaned. It has been found that, in operation, such membranes require a daily cleaning and that the pH and temperature of the effluents must be adjusted to about 9 or below and 125.degree. F., preferably about 100.degree. F., respectively, in order to prevent degradation (hydrolysis) of the membrane.
Since paper and pulp plant effluents can and do have a pH up to 14 and a temperature up to 180.degree. F., such effluents must be treated as noted above prior to ultrafiltration in order to lengthen the operational life of the cellulose acetate membranes. Attempts to substitute other membranes, such as fixed charge interpolymer membranes in place of the cellulose acetate membranes, have not proven successful. Such membranes have heretofore also not been capable of satisfactory performance at the high effluent pH's and temperatures.